The invention relates to a high-tensile brass alloy and a product, made of a high-tensile brass alloy, which is subjected to friction load.
For typical friction applications in a lubricant environment, alloys generally require low coefficients of friction. In addition, the coefficient of friction should be adaptable within predefined limits to the particular application, in particular the friction partner, the lubricant used, and the friction conditions, such as contact pressure and relative speed. This is true in particular for piston sleeves, which are acted on by high static and dynamic loads. In addition, applications with high relative speeds of the friction partners, as in axial bearings of a turbocharger, for example, require alloys which in addition to reduced heat generation also ensure good heat dissipation from the friction surface.
The friction power and the oil contact result in a tribological layer which has accumulated lubricant components on the bearing surface. A uniform, high deposition rate of the lubricant components and their breakdown products is necessary in order to obtain a sufficiently stable adsorption layer on the sliding layer.
A suitable bearing material is additionally characterized by wide-ranging oil tolerance, so that the structure of the tribological layer is largely insensitive to the selection of certain oil additives. A further objective is to provide an alloy for friction applications with good emergency running properties, so that a sufficient service life under dry friction conditions may be ensured.
For components under friction load, it is also important that the alloy used has sufficient strength. Accordingly, a high 0.2% yield strength should be present in order to minimize plastic deformations that occur under load. In addition, it is necessary to provide a particularly hard, high tensile strength alloy in order to increase the resistance of the alloy to abrasive and adhesive stresses. At the same, there must be sufficient toughness as protection against impact stresses. In this regard, it is necessary to reduce the number of microdefects and retard the resulting defect growth. This is accompanied by the requirement of providing an alloy having a preferably high fracture toughness which is largely free of internal stresses.
In many cases, suitable alloys for parts under friction load are special brasses, which in addition to copper and zinc as the primary components are alloyed with at least one of the elements nickel, iron, manganese, aluminum, silicon, titanium, or chromium. Silicon brasses in particular meet the requirements stated above; CuZn31Si1 represents a standard alloy for friction applications such as piston sleeves. Furthermore, it is known to use tin bronzes, which in addition to tin and copper additionally contain nickel, zinc, iron, and manganese, for friction applications or also for mining.
Reference is made to CH 223 580 A as an example of a copper-zinc alloy that is suitable for machine parts under stress from sliding, such as bearings, worm gears, gearwheels, slide shoes, and the like. The cited document discloses a copper content of 50-70 wt %, alloyed with 2-8 wt % aluminum, 0.05-3% silicon, and 0.5-10 wt % manganese, and the remainder zinc. In addition, the alloy may contain up to a maximum of 10 wt % lead as well as 0.1-5 wt % of one or more elements of the group comprising iron, nickel, and cobalt. Furthermore, a high-tensile brass alloy is known from EP 0 407 596 B1 which in addition to copper, zinc, manganese, aluminum, and silicon contains iron, nickel, and cobalt as optional alloy components. In addition, a content of 0.03-1 wt % oxygen is provided. Moreover, DE 15 58 467 A discloses another high-tensile brass alloy which is provided for objects under stress from sliding and friction. In addition to copper and a zinc content which may be as high as 45 wt %, alloy additives of manganese, silicon, and tellurium are present. In addition, Fe, Ni, Al, and Be represent further optional alloy components. Furthermore, DE 15 58 817 B2 and DE 101 59 949 01 describe copper alloys with a wide-ranging composition which form a reduced-wear bearing material.
To achieve certain properties of a product that is manufactured from a high-tensile brass alloy, alloys containing different alloy elements are used. Thus, for components of this type it is necessary to keep such different products in stock, and in particular to also be able to work with these various alloys.
The foregoing examples of the related art and limitations therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.